Identity management systems are information systems that support the management of identities. In particular, an identity management system establishes the identity of a subject or an object by linking a name (or number) with the subject or object. The identity management system may also describe the identity, for example, by assigning one or more attributes applicable to the particular subject or object to the identity. The identity management system may also modify the identity, such as by linking a new or additional name, or number, with the subject or object and/or change one or more attributes applicable to the particular subject or object. The identity management system can record and/or provide access to logs of activity by the identity.
One of the cornerstones of establishing a secure network environment is making sure that access is restricted to people who have the right to access the network. This access is allowed when the user can authenticate to the identity management system, meaning the user can verify his identity. The authentication may be managed by a public key infrastructure (PKI), such as implemented by a certificate system. For PKI, users and machines may present digital certificates to verify their identity. A digital signature is a mathematical representation of a message, using public key cryptography, which identifies the originator of the message, in a non-forgeable manner. Public key cryptography requires the use of two mathematically related keys—a public key and a private key (collectively referred to as a key pair). The private key is kept private by a single owner, and is not distributed to anyone else. The owner uses his or her private key, in conjunction with cryptographic algorithms, to digitally sign a message. The public key is made public, and can be used by anyone to verify the digital signature on a message. The fact that these two keys are mathematically related ensures that only a single private key can generate a digital signature that is verifiable by the corresponding public key, making the digital signature unforgeable. A digital certificate, commonly referred to as a certificate, is an electronic document used to identify an individual, a server, a company, or another type of entity and to associate that identity with a public key. The digital certificate binds a person's identity to his or her public key, and consequently, to his or her private key, and may be used to verify digital signatures. Digital certificates and digital signatures then provide the foundation for secure transactions over a network, such as the Internet.
Certificate authorities (CAs) validate identities and issue certificates. CAs can be either independent third parties or organizations running their own certificate-issuing server software, such as a certificate system. Before issuing a certificate, a CA must confirm the user's identity with its standard verification procedures. The certificate issued by the CA binds a particular public key to the name of the entity identified by the certificate. In addition to the public key, the certificates include the name of the entity it identifies, an expiration date, and the name of the CA that issued the certificate.
The CA can revoke a certificate or put a certificate on hold using a certificate revocation list (CRL). A CRL is a list of certificates that have been revoked or are no longer valid, and therefore should not be relied upon. The CRL may be a publicly available list of revoked certificates. A certificate is irreversibly revoked if, for example, it is discovered that the CA had improperly issued a certificate, or if a private-key is thought to have been compromised. Certificates may also be revoked for failure of the identified entity to adhere to policy requirements such as publication of false documents, misrepresentation of software behavior, or violation of any other policy specified by the CA operator or its customer. The most common reason for revocation is the user no longer being in sole possession of the private key (e.g., the token containing the private key has been lost or stolen). A certificate is put on hold to note the temporary invalidity of the certificate (e.g., if the user is unsure whether the private key has been lost). If, in this example, the private key was found and nobody had access to it, the status could be reinstated, and the certificate is valid again, thus removing the certificate from future CRLs.
A CRL issuer can publish a CRL immediately after a certificate has been revoked or released from being on hold. All CRLs have a lifetime during which they are valid (e.g., 24 hours or less). During a CRL's validity period, PKI-enabled applications may consult the CRL to verify a certificate prior to use. Conventional systems that publish the CRL every time a certificate is revoked or released from hold may engage a directory server for a considerable amount of time, especially if the CRL is large.